The most common human helminthic infection. Worldwide distribution. Highest prevalence in tropical and subtropical regions, and areas with inadequate sanitation. Occurs in rural areas of the southeastern United States.

Laboratory Diagnosis:Microscopic identification of eggs in the stool is the most common method for diagnosing intestinal ascariasis. The recommended procedure is as follows:

Collect a stool specimen. Fix the specimen in 10% formalin. Concentrate using the formalin–ethyl acetate sedimentation technique. Examine a wet mount of the sediment. Where concentration procedures are not available, a direct wet mount examination of the specimen is adequate for detecting moderate to heavy infections. For quantitative assessments of infection, various methods such as the Kato-Katz can be used. Larvae can be identified in sputum or gastric aspirate during the pulmonary migration phase (examine formalin-fixed organisms for morphology). Adult worms are occasionally passed in the stool or through the mouth or nose and are recognizable by their macroscopic characteristics.

TreatmentThe drugs of choice for treatment of ascariasis are albendazole* with mebendazole, ivermectin*, and nitazoxanide as alternatives. In the United States, ascariasis is generally treated for 1-3 days with medication prescribed by a health care provider. The drugs are effective and appear to have few side effects. For additional information, see the recommendations in The Medical Letter (Drugs for Parasitic Infections).

Life Cycle:

Adult worms live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with the feces . Unfertilized eggs may be ingested but are not infective. Fertile eggs embryonate and become infective after 18 days to several weeks , depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed , the larvae hatch , invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs . The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed . Upon reaching the small intestine, they develop into adult worms . Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female. Adult worms can live 1 to 2 years

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محمد نعيمعضو متألق

عدد المساهمات : 99تاريخ التسجيل : 26/03/2008العمر : 33

موضوع: رد: Ascariasis السبت أبريل 12, 2008 3:41 pm

Microscopy

Fertilized and unfertilized Ascaris lumbriocoides eggs are passed in stool of the infected host. Fertilized eggs are are rounded and have a thick shell with an external mammillated layer that is often stained brown by bile. In some cases, the outer layer is absent (known as decorticated eggs). Fertile eggs range from 45 to 75 µm in length. Unfertilized eggs are elongated and larger than fertile eggs (up to 90 µm in length). Their shell is thinner and their mammillated layer is more variable, either with large protuberances or practically none. Unfertile eggs contain mainly a mass of refractile granules. Complete development of the larva requires 18 days under favorable conditions (moist, warm, shaded soil). However, eggs of Ascaris lumbricoides may continue to develop and are infectious even when preserved in formalin